126 FOSSIL CRINOIDS. 



stems attached, from the same horizon and locality as the above mentioned 

 specimens of M. americanus. The calyx, so far as it can be seen, is identical 

 with them ; but the axial canal in the stem has three peripheral canals, instead 

 of four, as in the type. Upon this ground alone Miss Wood proposed for it the 

 genus Tripleurocrinus, with T. levis, as type. Now it is the fact that among the 

 peculiar assemblage of Crinoids belonging to this horizon of the Devonian, 

 having an unusual type of axial canal, there is a wide variation in the form of it, 

 not only within the same genus, but even the same species. In Cupressocrinus, 

 for example, it varies from three canals around a central one, to five. This 

 may be seen from Schultze's figures in his Monograph of the Echinoderms of 

 the Eifelkalk, viz: — 



C. crassus Taf . I, figs. 1/, ?n quadripartite. 



C. iiiflatus fig. 26 tripartite. 



C. hieroglyphicus fig. 3d tripartite. 



C. scaber fig, 46 quadripartite. 



C. abbreviatus Taf. II, fig. 6a quadripartite. 



C. elongatus Taf. Ill, fig. 16 quadripartite. 



C. gracilis fig. 2c . . . .tri-quadri- and quinquepartite 



in the same specimen. 

 Specimens of the same genus in my collection show variations as follows : — 



C. gracilis 5 specimens quadripartite; 2 tripartite. 



C. inflatus 1 " " 7 



C. sp. undescribed 3 " " 4 



Furthermore, my present material has produced a second quite distinct 

 species, doubtfully referred to SchuUzicrinus, from the same horizon and locality 

 as the tjTie species, and as M. americanus and T. lems, having a tripartite axial 

 canal, which cannot be placed in the same genus with the latter. In view of 

 these facts the genus Tripleurocrinus, having no other distinctive character 

 than its three peripheral canals, cannot be upheld; and I see nothing in the 

 specimen, which I have figured on Plate III, figs. 10a, 6, to distinguish it from 

 Myrtillocrinus americanus, of which, however, it furnishes the arm characters, 

 hitherto unknown. They are heavy, as indicated by the facets, apparently 

 simple throughout, and composed of brachials rather shorter than wide. 



A fact of no small interest prevailing throughout this grouj) of genera, is 

 the perforation of the radials and arms by a dorsal canal, — a feature which is 

 prevalent in the Recent Crinoids, but not found in many of the Palaeozoic. 

 It was strongly developed among the Devonian Inadunata, appearing in several 



